There is disclosed, in JP-A-2-205232, a forming method of forming a piece from a molten material without using a casting mold. This forming method is a modification of a so-called continuous casting method. In the continuous casting method, a molten metal is first solidified in a mold cavity formed through the casting mold which is positively cooled, and the solidified molten metal is then continuously drawn out from the mold cavity, whereby a piece having a large length is cast. In the forming method disclosed in the above publication, on the other hand, a restrictor frame is used in place of the casting mold. This disclosed forming method may be referred to as a continuous-drawing-up method. The restrictor frame is identical with the casting mold of the continuous casting method in that the restrictor frame has a mold cavity formed therethrough. However, in the disclosed forming method, the molten metal is solidified not in the mold cavity, but in a position located above the mold cavity.
The restrictor frame is a plate-like member having the mold cavity formed therethrough, and is disposed on the surface of the molten metal. Into the mold cavity of the restrictor frame, a comparatively narrow dummy bar made of the same material as the molten metal is introduced. This dummy bar is drawn up through the mold cavity, when the molten metal in the vicinity of the dummy bar is solidified into a forming starter member having a cross sectional shape which corresponds to the mold cavity. As the forming starter member is drawn together with the dummy bar upward through the mold cavity, the molten metal is also drawn owing to its surface tension so as to be located between the lower end of the forming starter member and the restrictor frame. That is, the drawn molten metal is located between the upper surface of the molten metal and a starter surface which is the lower end face of the forming starter member. In the initial period of the drawing process, the drawn molten metal is cooled indirectly through the forming starter member, thereby causing the drawn molten metal to be solidified gradually from the portion nearer to the forming starter member. In the subsequent period of the drawing process, the drawn molten metal is cooled indirectly through a formed piece which has been solidified from the drawn molten metal, thereby causing the drawn molten metal to be solidified gradually from the portion nearer to the formed piece. Thus, the drawn molten metal is solidified into the formed piece, which is then cooled by water and gas (for example, a nitrogen gas) respectively sprayed from a water spray nozzle and a gas spray nozzle. The drawn molten metal is continuously drawn upward, while being cooled as described above, so that the length of the formed piece is enlarged whereby a long piece is obtained.
In this continuous-drawing-up method in which the drawn molten metal located between the formed piece and the restrictor frame is solidified into the formed piece, the formed piece has a cross sectional shape corresponding to the cross sectional shape of the mold cavity of the restrictor frame. The continuous casting method in which the drawn molten metal is solidified in the casting mold, suffers from a drawback that friction between the formed piece and the casting mold causes the formed piece to be scratched at its surfaces, or causes the casting mold to be worn out. The continuous-drawing-up method in which the drawn molten metal is solidified into the formed piece outside the restrictor frame, on the other hand, is free from the above drawback encountered in the continuous casting method. Further, in the continuous-drawing-up method, since the drawn molten metal is solidified when the draw molten metal is not in contact with the restrictor frame, it is possible to obtain a high-quality piece constituted by column or structure formed as a result of solidification in one direction. Still further, in the continuous-drawing-up method, where the drawing velocity of the formed piece is held within an optimum range, it is possible to obtain a straight piece having cross sectional dimensions which are not diversified as viewed in the longitudinal direction. An increase in the drawing velocity provides a piece having a diameter which is reduced as viewed in a direction toward the top end of the piece. A reduction in the drawing velocity provides a piece having a diameter which is increased as viewed in the direction toward the top end of the piece.
However, the continuous-drawing-up method has a drawback that it is impossible to form a piece having a cross sectional shape which is other than the shape of the mold cavity formed through the restrictor frame. Namely, the restrictor frame has to be changed every time when the cross sectional shape of the formed piece to be formed is changed.
The invention of the present application has an object of obtaining a forming method and a forming system in which it is possible to easily form pieces having various cross sectional shapes, without changing the restrictor frame.